The present application relates to and incorporates herein by reference, Japanese Patent Application No. 2000-310940 filed on Oct. 11, 2000.
1. Field of the Invention
The present invention relates to a rotary electric machine mounted within a passenger car, truck or other vehicle.
2. Description of Related Art
In recent years, vehicle engine compartment volumes have decreased due to an increasing popularity of aerodynamic, sloped hoods and by the desire to increase passenger compartment space by utilizing space previously occupied by engine compartments. This has resulted in less space to mount engine components, and in particular, a vehicle engine alternator. Also, because of a desire to increase fuel economy of engines, engine rotation-per-minute (rpm) values have decreased in an effort to reduce engine cylinder firings while maintaining vehicle speed. Because of a decrease in engine rpms, alternator rpms have generally decreased. However, due to increased demand for devices such as safety control apparatuses that utilize electrical current, an increase in electrical current to energize the devices is desired. Therefore, it is desired to provide a small-sized, high power vehicle alternator to increase power generation capacity, yet provide the alternator at a low price.
Moreover, it is desired to decrease engine noise in response to consumer demand to decrease overall vehicular noise, including the noise level detectable in the passenger compartment. Therefore, the noise caused by fan blades or magnetic noise of the alternator which increases in direct proportion to engine speed, is desired to be reduced.
In a conventional vehicle alternator, a stator is constructed by winding a continuous wire around a stator core. A vehicle""s alternator structure must be improved in order to meet current requests which include small alternator size, high power generation, and reduced sound output levels.
Generally, in various rotary electric machines such as a vehicle alternator and the like, magnetic resistance exists because of an air gap between a rotor and a stator. Decreasing magnetic resistance on a magnetic excitation circuit will improve alternator performance. Therefore, in order to improve performance, it is desired to decrease the magnetic resistance by decreasing the size of the air gap and by increasing a facing area between the stator and the rotor. However, expansion of the facing area is limited due to a space restriction. Therefore, it is impossible to unlimitedly enlarge the facing area. Moreover, in consideration of a mechanical limitation such as component precision, assembling precision, and deformation of the rotor during rotation, a certain amount of air gap is necessary.
In the vehicle alternator, it is known that magnetic noise is decreased by suppressing excessive magnetic pulsations between the rotor and the stator core. This is normally accomplished by increasing the air gap between the rotor and the stator core. Thus, it is desired to increase the air gap in order to suppress the magnetic noise.
Further, in an air cooled type vehicle alternator, brine, slurry and other vehicle liquids may adhere to the facing surfaces of the rotor and the stator. In this case, the rotor is likely to lock due to corrosion generated on the rotor core and the stator core. Thus, it is undesirable to decrease the air gap by an extreme amount.
Therefore, in the conventional rotary electric machine, it is necessary to secure a predetermined air gap due to mechanical limitations, sound suppression, and to prevent the rotor from becoming locked by corrosion. Although it is desired to decrease the air gap on the magnetic circuit, it is impossible to decrease the air gap an extreme amount.
In view of the foregoing problems, it is an object of the present invention to provide a rotary electric machine in which an air gap is substantially decreased.
In the rotary electric machine according to the present invention, a rotor includes a rotor core alternately generating north and south (N/S) poles in a circumferential direction, and a field winding which is wound around the rotor core. Also, a stator includes a stator core arranged opposite to the rotor core and a stator coil wound around the stator core. The rotor and the stator are supported by a frame. A magnetic coating made of magnetic particles and a binding material, which binds the magnetic particles, is formed on at least one of the facing surfaces of the rotor core and the stator core which are opposite to each other. A tensile strength of the magnetic coating is designed to be lower than a bonding strength between the surface where the magnetic coating is formed and the magnetic coating. That is, if the magnetic coating is damaged by an external contact force, the magnetic coating will not break in the form of peeling from a surface of the core, but will break within the base material.
In this way, the magnetic coating is formed on one of the facing surfaces of the rotor core and the stator core, which are opposite to each other and define an air gap therebetween. That is, a magnetic substance exists in the air gap. Therefore, the air gap is equivalently decreased on the magnetic circuit. On the other hand, since the magnetic substance dispersedly exists in the magnetic member, the magnetic resistance on the magnetic circuit is not equal to that of the core. Therefore, there is no portion where a magnetic flux density is as high as that of the core. Accordingly, as compared with a case where the air gap between the opposing cores is small, there is no excessive magnetic pulsation so that the magnetic noise can be suppressed.
The above mentioned rotor has a pair of rotor cores including claw portions generating N/S poles and a boss portion comprising the field winding. The pair of cores are arranged oppositely to each other at an end surface of the boss portion to form a Lundell-type core. The magnetic coating is applied to at least one of the outer peripheral surfaces of the claw portions, the end surface of the boss portion, and an inner peripheral surface of the stator core. In the rotary electric machine having the Lundell-type core, the claw portions are deformed by receiving centrifugal force during rotation. Therefore, it is necessary to secure the air gap more than in other rotary electric machines. However, in the rotary electric machine of the present invention, the magnetic coating is formed on the surface of the cores which face the air gap. Therefore, in case the magnetic coating makes contact with each other or contact with the core in accordance with the rotation deformation of the rotor core, only a part of the magnetic coating is peeled and separates. Accordingly, the actual air gap can be set smaller.
Further, the rotor is composed of a first claw portion, a second claw portion, a boss portion and a field winding holding portion. The first claw portion is in a substantially cylindrical shape and produces N/S poles. The second claw portion holds the first claw portion through a non-magnetic member and is connected to a rotary shaft. The boss portion is arranged on an inner peripheral side of the field winding and is connected to the rotary shaft. The rotor winding holding portion holds the field winding and forms a magnetic circuit connecting the first claw portion and the boss portion. The magnetic coating is applied to at least one of the outer peripheral surfaces of the first and the second claw portions, an inner peripheral surface of the first claw portion, outer and inner peripheral surfaces of the rotor winding holding portion, and an inner peripheral surface of the stator core.
In this rotor used as a brushless generator, the claw portions are easily deformed due to centrifugal force during rotation. Therefore, it is necessary to set the air gap larger than that of a rotary electric machine having brushes. However, similar to the rotary electric machine having the Lundell-type core, the magnetic coating is formed on the surface of the core defining the air gap. Therefore, in case the magnetic member contacts other magnetic members or the core in accordance with the rotation deformation of the rotor core, only part of the magnetic coating peels and physically separates. Thus, the actual air gap can be set small.
The binding material is designed to be lubricious. Since the magnetic coating is made of a lubricated material such as grease and fills the air gap, the air gap can be substantially decreased to zero. That is, the air gap is at least minimized. Further, in the case where the rotor contacts the opposite stator core, because the magnetic coating is lubricious the possibility of problems such as noise or baking is likely to be decreased. Therefore, the distance between the rotor core and the opposing stator core is shortened.
Further, it is desired that the binding material also be an insulating material. It is known that unnecessary excess current occurs on the core surface where the magnetic flux changes, thereby deteriorating the efficiency of power generation. However, in the present invention, the magnetic coating made of the insulating material is formed on the surface of the cores so that occurrences of the excess current decrease and the output power can be increased.
Further, the above-described binding member is designed to also be a rust inhibitor. Since the rust inhibitor is placed on the surface of the cores, in the case that brine, slurry, and the like adhere on the core surfaces, rusting is inhibited. Accordingly, a locked rotor is prevented from occurring due to the prevention of corrosion from forming.